Sonic Depth Meter code & Math problems 12F683

[johnnylynx]

Have I defined my variables correctly?

[johnnylynx]

Sorry, and yes, runs once to establish one depth value based on the average of 10 readings. I have an external system that cycles the power every 5 min ultimately giving me an average reading every 5 min.

[Ioannis]

I 'd use what Henrik has posted and maybe with a smaller multiplier, say 3000. Keep your ten average pile. Then Henrik's lines will give you directly the result for your digital pot.

'Main Program  ****************************

'get avg depth
    pause 1000
    for x = 1 to 10
        pulsin gpio.4,1,inputpulse
        dist= dist + inputpulse
        pause 100
    next x
    
    newtapsetting = (dist ** 3060) - 42       'try also a number smaller, 3000
    IF newtapsetting > 127 THEN newtapsetting = 127

serout gpio.0,t9600,[12,"avg :", #avgdist,13]
serout gpio.0,t9600,["tap :", #newtapsetting]

pause 500

end

Ioannis

[johnnylynx]

Thanks guys. I'm trying to understand the math here, help me out.

What is the difference between * and **? I can't seem to find something on this forum that explains this. How does the math work.

For example, Henrik's suggestion above, how did you select 3060 to try and result in a range between 1 and 127? I tried random numbers and 2020 gets me close to my 127 value at full, but gives me 25 at empty. If I subtract 24 to give me 1, then I've also reduced my 127 to 103...Ugg.

and while I'm at it...how doe the */ and // work?


I really need the result to provide a linear value between 1 and 127 for this to work properly. So I feel like I need to determine the ratio of the reading (in this case with full reading 92 and emplty reading 364, I would subtract 91 from the values for an adjusted range between 1 and 273) then take the adjusted value and divide by 273 for a multiplier between 0 and 1 and apply that multiplier to 127.

[johnnylynx]

Excuse my last reply...Henrik's number of 3020 gets me a new tap setting of 127 (perfect empty value) but when the tank is full (8" away from the sensor) the new tap reading is 42 (not 0 or 1). If I subtract 42, the full reading gets to 0 or 1, but my empty reading is also reduced...not letting me see the empty value of 127.

[HenrikOlsson]

Hi,
I guess I'm a bit confused by your somewhat "conflicting" numbers.
In your original post you said that the input value ranged from 92 from to 466 but that a full scale output (127) should be reached with an input value of 364.

So, I need to convert the 92 and 364 to 1% or 100% respectively and apply to 127 to get a new tap setting

Think of the ** operator as kind of like multiplying by units of 1/65536. With an input value of 920 (given we stick with the times ten accumulated result) the output value would (should) be 920 * (3060/65536) = 42 and with an input value of 3640 the output value will be 3640 * (3060/65536) = 169. Subtract 42 from the two numbers and you'll get 0 and 127 respectively. Note that it's 3060, not 3020.

Is that not what you wanted? Or is that what you wanted but it doesn't actually give you those results - which is possible as I haven't tested it here. Please clarify.

The */ operator is similar to the ** operator but instead of units of 1/65536 it's units of 1/256. The // operator is modolus or remainder. If you do 123//10 you'll get 3 which is the "left over" from 123/10. They have been covered multiple times on the forum and they are covered in the manual.

/Henrik.

[Ioannis]

And if I may add, to prevent negative results, a limit test for the two sides of the range will guarantee the result will be 0-127.

Ioannis